Expression of key genes affecting artemisinin content in five Artemisia species

Artemisinin, an effective anti-malarial drug is synthesized in the specialized 10-celled biseriate glandular trichomes of some Artemisia species. In order to have an insight into artemisinin biosynthesis in species other than A. annua, five species with different artemisinin contents were investigated for the expression of key genes that influence artemisinin content. The least relative expression of the examined terpene synthase genes accompanied with very low glandular trichome density (4 No. mm^-2) and absence of artemisinin content in A. khorassanica (S2) underscored the vast metabolic capacity of glandular trichomes. A. deserti (S4) with artemisinin content of 5.13 mg g^-1 DW had a very high expression of Aa-ALDH1 and Aa-CYP71AV1 and low expression of Aa-DBR2. It is possible to develop plants with high artemisinin synthesis ability by downregulating Aa-ORA in S4, which may result in the reduction of Aa-ALDH1 and Aa-CYP71AV1 genes expression and effectively change the metabolic flux to favor more of artemisinin production than artemisinic acid. Based on the results, the Aa-ABCG6 transporter may be involved in trichome development. S4 had high transcript levels and larger glandular trichomes (3.46 fold) than A. annua found in Iran (S1), which may be due to the presence of more 2C-DNA (3.48 fold) in S4 than S1.